Posts Tagged Productivity

Qualities of Quality

[This is a slightly modified cross-post of something I wrote for the internal Spotify blog.]

I’m currently on parental leave, which is something that leaves very little time for any concentrated work effort because your first priority is to be on-call to solve the problems of a baby and you get interrupted all the time. But in between interruptions you can reflect on things and sometimes respond to email threads. I’ve been thinking about one topic in particular, namely quality, over the last week or two, and now my son is asleep, so I’m going to try to write up a blog post about it. In this post, I’m making the claim that

Developer-facing quality is a completely different thing from end-user facing quality, and is usually more important.

In one of the email threads I’ve been responding to at work, I said that “near-perfect quality code is … a meta-feature” meaning it affects and improves all other features, and that “it’s really a requirement to achieve sustainable speed”. I now think I can express that more precisely by considering different kinds of quality. The kind of quality I believe most people think about is what the end user experiences: product quality. Bugs, UI inconsistencies, etc. Product quality is a (non-functional) feature like any other, and can rightly be prioritised relative to other product features, such as performance, an improved design, a better recommendation algorithm and so on. The kind of quality that is a meta-feature is the quality a developer experiences, what I would term implementation quality. Things like readability and understandability of the code, ease of re-use, and bug-free-ness. Implementation quality doesn’t affect the end user experience, but it impacts the productivity of the teams working on improving the end user experience. These two kinds of quality overlap but are not the same:

Kinds of Quality

While a product can be compelling even if it has poor product quality and therefore a tradeoff between product quality and other product features is meaningful, it’s much harder to motivate not paying attention to implementation quality. Poor implementation quality kills your ability to add features and evolve your product and therefore makes poor product quality a much more serious problem. Poor implementation quality becomes an obstacle to changing your product, and changing the product quickly is key to getting it right.

A very closely related thought is Martin Fowler’s Design Stamina Hypothesis, which is an article you really should read and understand. So I’m not going to summarise it here, just go ahead and read it. Seriously, read it. Done? OK, now spend 4.43 minutes watching Ward Cunningham explaining (technical) debt. Even if you’ve watched that presentation before, it’ll be ~5 minutes very well spent.

Cunningham says that it can be a good idea to take on debt if you’re saying “I don’t understand this domain well enough to know that I’m building the right features or that I’m using the right abstractions for the features I’m building”. The first kind of debt is what Eric Ries is addressing in the lean startup movement, and what we’re addressing at Spotify with the Think It, Build It, Ship It, Tweak It mantra. The second kind is something you should take on and need to continually pay back as you get the required understanding of your domain. It’s not OK to take on debt by not following good engineering practices and, for instance, not cleaning up your code once you’ve made it work. It should be easy to understand the abstractions you’ve chosen, even if they’re not the right ones. Paying back debt should be mostly about fixing your design as you better understand what it should have been, not about fixing bugs or spaghetti code.

The two most important points Fowler makes, I think, are the narrowness of the time interval during which it is meaningful to trade off design/implementation quality for speed, and that once you’re past the point where the two curves intersect, continuing to disregard implementation quality just slows you down further. You can only profitably trade off implementation quality for speed in very short-lived projects. Probably, if you’re expecting a system to have a lifespan of more than a couple of weeks, it’s a good idea to pay attention to implementation quality right from the start. I think there may be exceptions, when you desperately need to get some feature out to survive. But most places are not struggling to survive from day to day, they’re doing things like figuring out how to build the best music streaming service in history. That’s hard, so we need to make sure that we can adapt our product quickly and easily as we learn how to do it.

In the figure above, I included simplicity as an aspect of both product and implementation quality. This is primarily due to a couple of thoughts: first, an article by Andres Kutt, where especially the section on what he calls functional architecture is relevant. The point he is making is that due to the huge number of features in the Skype web store, it ended up in a state where it was almost impossible to make changes to it. Feature count makes users confused (hence it’s a product quality issue) and it adds code complexity, making the code base less amenable to change. It’s a mistake to think that a feature is free just because you’re not doing active development on it.

A couple of notes on bugs. I include that in both product and implementation quality. The product perspective is pretty obvious – bugs detract from the user experience – but the implementation aspects may be a little less apparent. The first aspect is of course that it’s easier to build something on top of a solid component than a library. So if services and libraries are bug free, it’s easier to make sure that the end user experience is good. But there’s a second aspect as well. Bugs reduce productivity in many ways – for a longer discussion, see this post. The short of it is that unfixed bugs in your code lead to additional meetings, bug management overhead, duplicate reports of the same bug and context switching. So a lot of the time, the best thing you can do for your own productivity is to just fix pretty much everything that’s ever reported.

One common misconception about quality and its impact on delivery speed is that things like pluggability/extensibility/configurability of some technical solution are quality. Those are things often labelled as over-engineering. To me, over-engineering is engineers adding waste by inventing features that aren’t actually really needed. The notorious 2002 Standish Group report on feature use concluded that 64% of product features are rarely or never used. Considering that features interact in ways that make code less malleable, the best thing you can do for your own and your team’s productivity is to question any feature that goes into the product you’re working on. Especially if you came up with it yourself. At Spotify, product owners get their scope creep tendencies kept in check by Think It, etc., but nobody really checks that we engineers limit the scope of the code we write. Over-engineering is not about creating something with too good implementation quality, it’s creating something with too many features. In nearly two decades of doing professional software development, I don’t think I ever felt a team I worked in overspent seriously on implementation quality, but I’ve definitely many times felt that we’ve wasted hugely on some feature or other.

I’ve also got some opinions about the use of TDD to drive implementation quality, but my son is going to wake up any minute, so that will have to remain a topic for a future blog post. :) For now, a summary of this post in two bullet points – to be able to move fast with product development, you need to:

  • Be ruthless about minimising the feature count, and
  • Always pay very close attention to implementation quality – but feel free to trade off product quality if needed.

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Product Development vs Productivity Development

A couple of years ago, the team I was in started to use a concept we called gradual refactoring, whereby we would allocate a fixed percentage of our capacity to doing refactoring in order to keep technical debt at bay. That worked pretty well, and has been refined over the years into something we now tend to call the Productivity Backlog, in contrast to the normal Product Backlog. The way we use this idea boils down to reserving a more-or-less fixed percentage of overall capacity to improving that capacity. This is typically refactoring or cleaning up old, hard-to-change code or building or improving tools to help with something that slows us down. Normally those tools help us automate some process, making it less error-prone and less labour-intensive.

This works really well. Initially, I wanted to keep productivity efforts as part of the normal backlog, because I wanted a global prioritisation order. “All we need is to get really good at weighing medium to long-term benefits of productivity improvements vs the shorter term benefits from the product improvements”. That has turned out to be even harder in practice than I had thought. It’s just easier to keep things separate, for the following reasons:

  • It’s an easier sell to the non-technical parts of/people in the organisation. “Continuous improvement” is something almost all organisations would like to do, and keeping a Productivity Backlog is an easy way to formalise that at a team level.
  • It means that, as a technical person, you don’t have to try to sell the benefits of intangible things like “refactoring” or “eliminating technical debt” each time you need to untangle something particularly troublesome in your code base.
  • It means that, as a business person, you don’t need to try to understand the reasons why some code is poorly suitable to some task or other, freeing you up to focus more clearly on figuring out what features and changes will make the product more successful in the future.
  • It simplifies prioritisation both on the product and the productivity side, because a) you are comparing apples with apples (or at least fruits with fruits, if you know what I mean) on both backlogs and b) you can have different owners who can structure and order their own backlog without a need to coordinate needs and requirements from the other one.
  • It provides an easy knob to turn as needs change – if you urgently need to get some product feature out, you can easily turn the productivity backlog down to 10% or even 5%. And if you’re suffering acutely from wasted time due to inefficient deployment procedures, you can turn it up to 20-25% until you’ve solved that crisis. If you do things on a case-by-case basis, you have to weigh the benefits of saving 3 minutes each time somebody needs to deploy a particular build of something somewhere against trying out a new front page to improve conversion, something that is hard and requires people with different types of expertise to understand each other’s problems and agree to a compromise.

Some of the issues we’ve had in using this concept have been around figuring out what types of changes should go on it. Initially, we called it the ‘tech backlog’, because it was owned by ‘tech’ and dealt very much with issues in implementation. That led to attempts at adding things like performance problems/measurement, or bug fixes driven more by technology than by the business side of things (like things getting logged that made real problems hard to find even though there was no obvious end-user impact). But those things are product features – quality and performance are clearly features in the product. Productivity is about the team’s ability to deliver more product features over time. That means it can be about fixing bugs, if those bugs, for instance, mean that deployment occasionally fail. But most of the time, it’s about removing obstacles and frustrations that keep us from delivering the product improvements that are what we get our job satisfaction from.

Productivity backlogs, compared to product backlogs, are reactive more than proactive. You feel the pain of some faulty process or code, and when it grows unbearable, you add fixing it near the top of your productivity backlog. There’s very little point in having long term goals for a productivity backlog.

A separate productivity backlog makes life simpler for both the business and the delivery side of things, is a great way to formalise continuous improvement and helps improve job satisfaction in delivery teams partly by removing obstacles to productivity and partly by providing knowledge (or hope at least) that the muck you’re having to wade through at the moment will at some point in the future be cleared out. Everybody should have one!

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If it’s Broken, Fix It

A search for terms like “bug classification” or “bug priority” gives a lot of results with lots of information about how to distinguish bug severity from bug priority, methods to use to ensure that you only fix the relevant bugs, what the correct set of severities are (is it Blocker, Major, Minor, Cosmetic, or should there be a Critical in there as well?), and so on. More and more, I’m starting to think that all that is mostly rubbish, and things are actually a lot simpler. In 95% of the cases, if you have found a bug, you should fix it right then and there, without wasting any time on prioritising or classifying it. Here’s why:

Cost of fixing or leaving a bug

Fixing a bug means you incur a cost, and that’s the reason why people want to avoid fixing bugs that aren’t important. Cost-cutting is a great thing. The problem is, not fixing a bug also has a cost. If you decide to leave some inconsequential thing broken in your system, most likely, you’ll run into the same thing again three months down the line, by which time you’ll have forgotten that you had ever seen it before. Or, equally likely, somebody else will run into it next week. Each time somebody finds the thing again, you’ll waste a couple of hours on figuring out what it is, reporting it, classifying and prioritising it, realising it’s a dupe, and then forgetting about it again. Given enough time, that long term cost is going to be larger than the upfront fixing cost that you avoided.

What’s more, just having a process for prioritising bugs is far from free. Usually, you will want the person who does the prioritisation to be a business guy rather than a QA or development guy. Maybe the product owner, if you’re doing Scrum. That means that for every bug, she will have to stop what she is doing, switch contexts and understand the bug. She will want to understand from a developer if it is easy or hard to fix, and she will want to assess the business cost of leaving it unfixed. Then she can select a priority and add it to the queue of bugs that should be fixed. In the mean time, work on the story where the bug was found is stalled, so the QA and developer might have to context switch as well, and do some work on something else for a while – chances are the product owner won’t be available to prioritise bugs at a moment’s notice. Instead, she might be doing that once per day or even less frequently. All this leads to costly context switching, additional communication and waiting time.

The solution I advocate is simple: don’t waste time talking about bugs, just fix them. The majority of bugs can be fixed in 1-5 hours (depending of course on the quality of your code structure). Just having a bug prioritisation process will almost certainly take 1-3 man-hours per bug, since it involves many people and these people need to find the time to talk together so that they all understand enough about the problem. The cost might be even larger if you take context switching and stall times due to slow decision-making into account. And if you add the cost of having to deal with duplicate bugs over time, it’s very hard to argue that you will save anything by not fixing a bug. There are exceptions, of course. First, time is a factor; the decision not to fix will always be cost effective from a very short perspective, and always wasteful from a very long perspective. Second, the harder the bug is to fix, and the less likely it is to happen, the less likely is it that you’ll recover the up-front cost of fixing the bug by avoiding long-term costs due to the bug recurring. I think it should be up to the developer whose job it is to fix the bug to raise his hand if it looks likely to fit into the hard-to-fix-and-unlikely-to-happen category. My experience tells me that less than 5% of all bugs fit into this bucket – I just had a look at the last 40 bugs opened in my current project, and none of those belonged there. Anyway, for those bugs, you will need to make a more careful decision, so you need the cost of a prioritisation process. That means you can reduce the number of bugs you have to prioritise by a factor 20, or perhaps more. Lots less context-switching and administration in the short perspective, and lots less duplicated bug classification work in the longer perspective.

Note that the arguments I’m using are completely independent of the cost of the bug in terms of product quality. I’m just talking about development team productivity, not how end users react to the bug. I was in a discussion the other day with some former colleagues who were complaining that the people in charge of the business didn’t allow them to fix bugs. But the arguments they had been using were all in terms of product quality. That is something that (rightly, I think) tends to make business people suspicious. We as engineers want to make ‘good stuff’. Good quality code that we can be proud of. But the connection between our pride in our work and the company’s bottom line is very tenuous – not nonexistent, but weak. I want to be proud of what I do, and what’s more, I spend almost all of my time immersed in our technical solutions. This gives me a strong bias towards thinking that technical problems are important. A smart business person knows this and takes this into account when weighing any statement I make. But to me, the best argument in favour of fixing almost all bugs without a bug prioritisation process only looks at the team’s productivity. You don’t need the product quality aspect, although product quality and end-user experience is of course an additional reason to fix virtually all bugs.

So, it is true that there are cases when you want to hold off fixing a bug, or even decide to leave it in the system unfixed. But those cases are very rare. In general, if you want to be an effective software development team, don’t make it so complicated. Don’t prioritise bugs. If it’s broken, fix it. You’ll be developing stuff faster and as an added bonus, your users will get a better quality system.

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Testing and Code Correctness

Lately, I’ve found myself disagreeing with such giants as Trygve Reenskaug and Tony Hoare, and thinking that I have understood something about software that maybe they have not. A nobody disagreeing with two famous professors! Can I have a point? Well, read on and make up your own mind about it.

Since discovering about Trygve’s brainchild DCI, I’ve been following the discussions on the Object Composition discussion group. I’m not participating actively in the discussions; the main reason for me following the group is that Trygve is active there, and he has a lot of profound insights into software development which makes reading his posts a joy. But I’ve found myself disagreeing with him on one or possibly two closely related points. In at least one of his talks, he makes the point that testing does not help you get quality into a product. All tests do is prove that a particular execution path with particular parameter values works, they say nothing about what will happen if some parameter values change, and no matter how much you test some code, you can’t say that it is bug-free. Instead, the way to get quality into code is through readability. He often quotes Tony Hoare, who said:

“There are two ways of constructing a software design: One way is to make it so simple that there are obviously no deficiencies and the other is to make it so complicated that there are no obvious deficiencies.”

This is a lovely and memorable quote, but as all soundbites, it is a simplification. In fact, I think it is simplified to the point of not being meaningful, and while I think that Trygve’s point about testing is correct, I also think it is not very important and a slightly dangerous point to make as it might discourage you from testing. Tests, especially automated ones, are critical when building quality software, even though they don’t put quality into the product. Let me start on why I don’t think Tony Hoare’s quote is great with two code examples.

Some code that works

public class Multiplier {
   private static final double POINT_25 = 0.25;

   public double multiplyByPoint25(double amount) {
      return amount * POINT_25;

This code is simple, to the point where it obviously contains no deficiencies. It’s not particularly interesting, but a glance shows that it does what you’d expect it to. One point to Tony!

Some code that is broken

public class VatCalculator {
   private static final double VAT_RATE = 0.25;

   public double calculateVat(double amount) {
      return amount * VAT_RATE;

This code is broken in at least two ways:

  1. It does monetary calculations using floating-point arithmetic. This means that calculations aren’t exact, and exactness is always a requirement when dealing with money (see for instance Effective Java, Item 48 for more on this).
  2. It is probably broken in more subtle ways as well. In Sweden, the default VAT rate is indeed 25% on top of the price before VAT. But most of the time, people in Sweden think about this backwards – the only price they see is the one with VAT, so some people prefer to multiply the total price by .2 to get the part of the total price that is VAT. We don’t know if the amount is the amount before VAT or the total amount including VAT. Also, the VAT rate depends on the item type, so if this method were called using the price of a pencil, it would probably give the right answer, but it wouldn’t for a book. And if the amount is the total of an order for a pencil and a book, it’s wrong in yet another way. The list of things that could be broken in terms of how to do VAT calculations goes on.

And the funny thing is, from a machine-instructions perspective, the two classes are of course identical! Why is the first one right, and the second one wrong, just because we changed some names? When the names changed, our perception of the programmer’s intent changed with them. Suddenly, the identical machine instructions have a more specific purpose, and we see more of the actual or probable business rules that should be applied. This makes the second version obviously broken because it uses floating-point arithmetic for monetary calculations. We understand enough about the programmer’s intent to find a mistake. But while the floating-point error is obvious, there is nothing in the code that gives us clear evidence as to whether the VAT calculation is correct in terms of the rate that is being applied or not.

Clearly, readability is not sufficient to guarantee correctness. Correct code meets its business requirements – the intent of the person who uses it for something. Readability can at best tell us if it meets the intent of the programmer that wrote it. This doesn’t mean readability is unimportant; on the contrary, readable code is a holy grail to be strived for at almost all cost. But it does mean that Tony Hoare’s goal is unachievable. The code by itself cannot “obviously have no deficiencies”, because the code only tells us what it does, not what it should do.

Testing to the Rescue

So how can we ensure that our code is correct? Well, we need well-defined requirements and the ability to match those requirements with what the code does. There are people whose full-time job is to define requirements; all they do is to formulate business users’ descriptions of what they do in terms that should be unambiguous, free of duplication, conflicts, and so on, so that programmers and testers can get a clear picture of what the code should actually be doing. There are whole toolsets for requirements analysis and management that help these people produce consistent and unambiguous definitions of requirements. Once that’s done the problem is of course that it’s really hard to know if your code actually meet all the requirements that are defined. No problem, there’s further tools and processes that support mapping the requirements to test cases, executions of these test cases and the defects found and fixed.

Like many others (this is at the heart of agile), I think all that is largely a waste of time. I’m not saying it doesn’t help, it’s just very inefficient. It’s practically impossible to formulate anything using natural language in a way that is unambiguous, consistent and understandable. And then mapping requirements defined using natural language to tests and test executions is again hard to the point of being impossible. The only languages we have that allow us to formulate statements unambiguously and with precision are formal systems such as programming languages. But wait, did I just say we can write something that has no ambiguity in code? Could we formulate our requirements using code? Yes, of course. Done right, that’s exactly what automated tests are.

If our automated tests reflect the intent of the users of the code, we can get an extremely detailed and precise specification of the requirements that has practically zero cost of verification. Since the specification is written in a programming language, it is written using one of the best tools we know how to design in terms of optimal unambiguity and readability. As we all know, programming languages have shortcomings there, but they are way superior to natural language.

The argument that business users won’t be able to understand tests/requirements written in code and that they therefore must be in natural language is easy to refute on two grounds: first, business users don’t understand a Word document or database with hundreds or thousands of requirements either (and neither do programmers), and second, let the code speak for itself. Business users can and do understand what your product does, and if it does the wrong thing, they can tell you. Fix the code (tests first), and ship a new version. Again, a core principle in agile.

I often come across a sentiment among developers that tests are restrictive (“I’ve fixed the code, why do I have to fix the test too”), or that you “haven’t got the time to write tests”. That’s a misunderstanding – done right, tests are liberating and save time. Liberating, because the fact that your tests specify how the code is intended to behave means that you don’t need to worry as much about breaking existing functionality. That enables you to have multiple teams co-owning the same code, which improves your agility. Maybe even more importantly, having a robust harness of tests around some code enables you to refactor it and thereby keep the code readable even in the face of evolution of the feature set it must support.

So that should hopefully explain why I think the point that Trygve made about tests not being able to get quality into a product is valid but not really important. The quality comes from the clarity of the system architecture, system design and code implementation, not from the tests. But automated tests enable you to keep quality in a product as it evolves by preventing regression errors and making it possible for you to keep the all-important clarity and readability up to date even as the code evolves.


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Making No Mistakes is a Mistake

Here’s one of my favourite diagrams:

What it shows is an extremely common situation – an axis, where one type of cost is very large at one end of the scale (red line), and a conflicting type of cost is very large at the other end of the scale (green line). The total cost (purple line) has an optimum somewhere between the extremes. I mentioned one such situation when talking about teams working in isolation or interfering with each other. To me, another example is doing design up-front. If you don’t do any design before starting to write a significant piece of code, you’re likely to go very wrong – if nothing else, in terms of performance or scalability, which are hard to engineer in at a late stage. But on the other hand, Big Design Up Front typically means that you waste a lot of time solving problems that, once you get down to the details, turn out never to have needed solutions. It’s also easier to come up with a good design in the context of a partially coded, conctrete system than for something that is all blue-prints and abstract. So at one end of the scale, you do no design before you write code, and you run a risk of incurring huge costs due to mistakes that could have been avoided by a little planning. And at the other end of the scale, you do a lot of design before coding, and you probably spend way too much time agonizing over perceived problems that you in fact never run into once you start writing the code. And somewhere in the middle is the sweet spot where you want to be – doing lagom design to use a Swedish term.

The diagram shows a useful way of thinking about situations for two reasons: first, these situations are very common, so you can use it often, and second, people (myself very much included) often tend to see only one of the pressures. “If we don’t write this design document, it will be harder for new hires to understand how the system works, so we must write it!” True, but how often will we have new hires that need to understand the system, how much easier will a design document make this understanding, and how much time will it take to write the document and keep it up to date? A lot of the time, the focus on one of these pressures comes from a strong feeling of what is “the proper way to do things”, which can lead to flame wars on the web or heated debates within a company or team. An awareness of the fact that costs are not absolute – it is not the end of the world if it takes some time for a new hire to understand the system design, and a document isn’t going to make that cost zero anyway – and of the fact that there is a need to weigh two types of costs against each other can make it easier to make good decisions and have productive debates.

For me, a particularly interesting example of conflicting pressures is where work processes are concerned. I think it is fair to say that they are introduced to prevent mistakes of different kinds. With inadequate processes, you run a risk of losing a lot of time or money: lack of reporting leads to lack of management insight into a project, which results in worse decisions, lack of communication means that two people in different parts of the same room write two almost identical classes to solve the same problem, lack of quality assurance leads to poorly performing products and angry customers, etc. On the other hand, every process step you introduce comes with some sort of cost. It takes time to write a project report and time to read it. Somebody must probably be a central point of communication to ensure that individual programmers are aware of the types of problems that other programmers are working on, and verifying that something that “has always worked and we didn’t change” still works can be a big effort. So we have conflicting pressures: mistakes come with a cost, and process introduced to prevent those mistakes comes with some overhead.

As a side note, not all process steps are equal in terms of power-to-weight ratio. A somewhat strained example could be of a manager who is worried about his staff taking too long lunch breaks. He might require them to leave him written notes about when they start and finish their lunch. The process step will give him some sort of clearer picture of how much time they spend, but it comes at a cost in time and resentment caused by writing documents perceived as useless and an impression of a lack of trust. An example of a good power-to-weight ratio could be the daily standup in Scrum, which is a great way of ensuring that team members are up to date with what others are doing without wasting large amounts of time on it.

Getting back to the main point: when adopting or adapting work processes, we’ll want to find a sweet spot where we have enough process to ensure sufficient control over our mistakes, but where we don’t waste a lot of time doing things that don’t directly create value. Kurt Högnelid, who was my boss in 1998-1999, and who taught me most of what I know about managing people, pointed out something to me: at the sweet spot, you will make mistakes! This is counter-intuitive in some ways. During a retrospective, we tend to want to find out what went wrong and take action to prevent the same thing from happening again. But this diagram tells us that is sometimes wrong – if we have a situation where we never make mistakes, we’re in fact likely to be wasteful in that we’re probably overspending on prevention.

Different mistakes are different. If the product at hand is a medical system, it is likely that we want to ensure that we never make mistakes that lead it to be broken in ways that might harm people. The same thing is true of most systems where bugs would lead to large financial loss. But I definitely think that there is a tendency to overspend on preventing simple work-related mistakes through for instance too much planning or documentation, where rare mistakes are likely to cost less than the continuous over-investment in process. It takes a bit of daring to accept that things will go wrong and to see that as an indication of having found the right balance.


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Gradual Refactoring

We’re right now in the middle of something that feels a little like an unplanned experiment in code management. Unplanned in the sense that I didn’t expect us to work the way we do, not so much in the sense that I think it is particularly risky. It started not quite a year ago with my colleague Mateusz suggesting that we should dedicate a fixed percentage of the story points in each sprint to what he called maintenance or technical stories. That soon crystallised into a backlog owned by me, where we schedule stories that are aimed at somehow improving our productivity as opposed to our product. So Paul, the ‘normal’ product owner, is in charge of the main backlog that deals with improving the products, and I am the owner of the maintenance backlog, where we improve the efficiency of how we work by improving processes, tools and removing technical debt. We’re aiming at spending about 15% of our time on technical backlog stories, and we more or less do.

Typical examples of stories that have gone onto our technical backlog are:

  • A tool that allows QA to specify that outgoing service calls matching certain regular expressions should return mock data specified in a file rather actually calling the service. This makes us a lot more productive with regard to verifying site behaviour in certain hard-to-recreate and data-dependent cases.
  • Improvements to our performance monitoring systems and tools that make it easier for us to figure out where we have performance problems when we do.
  • Auditing and optimising the QA server allocation in order to speed up especially our automated test scripts.
  • Various refactoring stories that clean up code where functional evolution has led to the original design no longer being suitable.

That has worked out pretty much as expected: we’ve gained benefits from the productivity improvements and we continue to spend 5-6 times more effort on money-making product improvements than on engineering driven platform-building.

The unexpected thing that has happened is that we’re heading towards a situation where we have different design generations that solve similar problems. As an example, the original pattern we used to create Spring MVC controllers has broken down, so we’ve come up with a new one that is better though not yet perfect. In order to have stories small enough to complete within one iteration, we’ve had to apply this pattern on a controller-by-controller basis – each refactoring has taken about 2 weeks of calendar time so far, except the first one which took about 4, so the effort isn’t trivial. There are nearly 40 controller implementations in our site code and about 95% of the incoming traffic is handled by 4 of those. We’re now at a stage where we’ve refactored three of those four controllers. Given that the other 35 or so controllers a) don’t serve a lot of traffic, so don’t have a lot of business value and b) don’t get changed a lot because the functions they provide aren’t ones that we need to innovate in, I don’t feel like refactoring all of them. In fact, the next refactoring story in the backlog is aimed at a different area in the site, where a repeated pattern has broken down in a similar way.

My initial gut reaction was that we should apply any new pattern for a commonly occurring situation across the board, then tackle the next similar situation. That keeps the code clean and makes it easy to find your way around. But the point of refactoring is that it must be an investment that you can recoup, and if we haven’t spent more than 4 hours working on a particular controller in the last year, what are the chances of ever recouping an investment of a man-week? We would probably have to keep using the same controller for at least 20 years, assuming the refactoring made us twice as productive, and that doesn’t seem likely to happen. Given that, it seems like the best option is to focus refactoring efforts where they give return on investment, which is those parts of the code that you do most of your work in.

I think we’re more or less permanently stuck with two different generations of controller patterns. But it will be interesting to see what will happen over the next year or two – can this super-pattern of having annual growth rings of standardised solution patterns handle more than two generations? I’m not sure, but I believe it can.


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Code Sharing: Use Scrum

(This is item 3 in the code sharing cookbook)

Today, no CV comes along without “Scrum” and “Agile” on it and Scrum has gained acceptance so quickly that it should definitely set off any hype-warning systems. I personally think there’s a lot more to Scrum than just a hype – if you do it right, it’s extremely useful for productivity. There are some aspects of Scrum done right that are particularly valuable for sharing code:

  • Empowering teams to deliver end-to-end functionality.
  • (Relatively) short iterations.
  • Delivering potentially shippable results with every sprint.

The biggest one is empowering teams to deliver fully functioning features. The way I think that affects code sharing is that rather than having your organisation focus on developing technology horizontals, you aim at developing feature verticals.

As much as feasible, Scrum tells you to have teams whose focus is to deliver the blue verticals in the above diagram. The red horizontals will be developed and maintained as a consequence of needs driven by the products. At the other end of the spectrum, your teams are aligned along the libraries or technology components, with each team responsible for one or more services or libraries. Obviously, you can vary your focus from totally red to totally blue, and you get different advantages and disadvantages depending on where you are. At the ‘red’ end of the spectrum, with teams very much aligned along technical component lines, you get the following advantages and disadvantages:

  • Teams get a very deep knowledge of their components leading to solid, strong technology.
  • Teams get a strong feeling of ownership of components, and can take a long view when developing them.
  • You need to align product roadmaps for different products so that they can take advantage of features and changes made in the underlying libraries.
  • You will get queues and blockages in the product development, where one team is waiting for the result of another team’s work, or where one team has finished its work and the result “sits on a shelf” until the downstream team is ready to pick it up. (This is what Lean tells you to avoid.)
  • Most teams are not customer-facing, meaning that their priorities tend to shift from what is important to the business to what is important to their component. This in turn increases the risk of developing technology for its own sake rather than due to a business need.

At the ‘blue’ end, on the other hand, shared code is collectively owned by multiple teams and you get a situation where:

  • Teams rarely need to wait for others in order to get their features finished and launched. This is great for innovation.
  • The fact that there is never any waiting and the teams are typically in control of their own destiny is energising: nobody else is to blame for failures or gets credit for successes. Work done leads to something visible. This makes it more rewarding, fun and efficient.
  • Features and changes that are developed are typically well aligned with business priorities.
  • There is a real risk of under-investing in shared technology. Larger restructuring tasks may never happen because no single team owns the responsibility for technology components.
  • There is no roadmap for individual components, which can lead to bloat and sprawl.
  • The lack of continuity increases the risk that it is unclear how some feature was intended to work and the reasons why it was implemented in a certain way are more likely to be forgotten.
  • Developers (by which I don’t mean just programmers, but all team members) need to be jacks-of-all-trades and risk being masters of none.

I think that the best solution in general is to get redder the deeper you go in the technology stack, because that’s where you have more complex and general technologies that a) need deep knowledge to develop and b) typically don’t affect end-user functionality very directly. I also think that most organisations I’ve seen have been too red. Having product-specific teams that are allowed to make modifications to much of the shared codebase allows you to develop your business-driving products quickly and based on their individual needs. So there should be more focus on products and teams that can develop features end-to-end, just as Scrum tells us!

The next thing that makes Scrum great for sharing code is the combination of time-limited sprints and the focus on delivering finished code at each iteration. The ‘deliver potentially shippable code’ bit seems to be one of the hardest things about Scrum, even though it is actually quite trivial as a concept: if you don’t feel like you could launch the code demoed at the end of the sprint the day after, don’t call the story done, and don’t grant yourself any story points for it. That way, you’ll not be able to let anything out of your sights until it is shippable and your velocity will be reduced until you’re great at getting things really ready – which is exactly right! If it is difficult for your team to take things all the way to potentially shippable because of environmental or process problems, then fix those issues until it is easy.

Actually finishing things is great for productivity in general, but it is even better in a code-sharing context. To illustrate how, I’ll use one of my favourite diagrams:

Assume you have three features to complete, each of which requires three tasks to be done. Each of the tasks takes one day, and you can only do one task at a time. If, as above, you start each feature as early as possible, all the code that is touched by feature A is in a ‘being modified’ state for 7 days (from the start of A1 to the end of A3), and the same applies to features B and C. In the second version below, the corresponding time is 3 days per feature, meaning that the risk that another team will need to make modifications concurrently is less than half of the first version.

Also, having any updates to shared code completed quickly means that the time between merge opportunities is decreased, which decreases the risks of isolation. You really want to shorten the branch – modify – merge back cycle as much as possible, and Scrum’s insistence on getting things production-ready within the time period of a single sprint (which is supposed to be less than 4 weeks – I’ve found that 2 or 3 weeks seems to work even better in most situations) is a great support in pushing for a short such cycle.

I think Scrum is great in general, and done right, it also helps you with sharing code. Jeff Sutherland said in a presentation I attended that the requirement to produce potentially shippable code with each iteration is the hardest requirement in the Nokia test. I can reluctantly understand why that’s the case. It’s not conceptually hard and unlike some classes of technical problem, it doesn’t require any exceptional talent to succeed with. What makes it hard is that it requires discipline and an environment where it is OK to flag up problems without management seeing that as being obstructive. It’s worth doing, so don’t allow yourself any shortcuts, and fix every process or environment obstacle that stands in the way of producing shippable code with each sprint. Combine that with teams that are empowered to own and modify pretty much all the code that makes up their product, and you’ve come a long way towards a great environment for code sharing.

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Just Do It – or Not

I just found myself disagreeing with me. I reread a blog post that I had written a week or two ago that was posted on the Shopzilla blog, and noticed that I had written that “metadata is as important as the primary data (well, close enough that the difference doesn’t really matter)”. That was wrong. There is actually no difference in importance between the two. This is because importance is actually binary: either you have to do something, or you don’t.

I’ve found myself using more fine-grained definitions of relative importance of things before, and I thought it was a good thing to do. Having different severity levels for bugs, for instance, felt right: there seemed to be a difference between a blocker, a normal-level one and a cosmetic bug. Over time, I’ve come to realise that there are only two classes of bugs: those you can live with and those you can’t. The latter must be fixed, the former don’t have to be. And the corollary of that is that it’s always going to be more important to add another feature than to fix a bug that you can live with, so the bugs you don’t have to fix should just be put into some bucket where they can live undisturbed forever.

I remember some years ago, when Microsoft released a Windows version that had something like 35,000 known bugs in it, and how some people were upset about that. “How can they release something that has so many bugs?” I think that is (or at least can be) a perfectly OK thing to do, it just means that you’ve tested your software thoroughly and know the quality status of it. The remaining bugs are things you’ve decided not to fix.

Getting back to the topic of priority again: that is another thing, it’s not the same as importance. I think of it as a two-dimensional thing, where importance is one axis and urgency is the other. Say you have five things to do, A through E. As soon as you get E done, you’ll increase your revenue by around 3%, but before you can do E, you need to do D. A is a bug that you really want to fix, B is a document that you ought to write according to the company standard process, but that nobody will ever read, and C is a bug that you in all honesty don’t need to fix even if it annoys you. This diagram shows how I would do prioritisation in that case.

How importance and urgency make priority

The unimportant things get an urgency of zero. We don’t need to do them, so let’s just not do them (although the best thing to do about that document is to change the company process that requires doing work that is wasteful). The urgency values assigned to the important things are based on their intrinsic value and on dependencies between them.

I’ve been guilty of the sin of having lots of half-finished items on my daily todo-list. Often, the reason why I didn’t finish those things was that they were actually not that important, but I still didn’t take them off the list. This led to more stress and ‘mental overhead’. It is a common situation, I think. I also think it is very detrimental to productivity. If you want to be great at executing, I think that a certain ruthlessness about deciding what should be done – and more to the point, what should not – and lots of discipline about actually doing it is necessary. Here are two rules I try to follow:

  1. If you have to do it, just do it – and finish it. Really. All the way.
  2. If you don’t have to do it, there’s no excuse for doing it. So don’t even think about it – put it on a pile of stuff that you can forget about and make sure it doesn’t worry you.